Laser Power Calibration in an Optical Disc Drive

ABSTRACT

Various systems, methods, and programs embodied on a computer-readable medium are provided for calibrating a laser power in an optical disc drive. In one embodiment, a range of reflectivity of an optical disc in the optical disc drive is established. A calibration pattern of marked segments is written to the optical disc and the reflectivity of the marked segments is measured. An average reflectivity is generated for each one of a plurality of laser power settings within the range of reflectivity, thereby obtaining a curve that depicts the average reflectivity with respect to the laser power settings. The laser power setting at a knee of the curve is identified and a slope of the curve at a position on the curve where the average reflectivity decreases as the laser power settings increase is determined. The laser power setting is calculated that results in a predefined darkness based upon the laser power setting at the knee and based upon the slope.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending US Patent Application entitled“Laser Power Calibration in an Optical Disc Drive” filed on even dateherewith and assigned application Ser. No. ______ (Attorney DocketNumber 100200325-1).

BACKGROUND

Some optical disc drives may be employed to both read and write data toan optical disc, and to write a label to an optical disc. When opticaldisc drives are manufactured at a factory, a power of a laser includedin the optical disc drive may be optimized for the best performance, forexample, in writing labels to optical discs. However, when an opticaldisc drive is used over time, degradation in the ability to write labelsto optical discs inevitably occurs. For example, dust and otherparticles may collect on lenses associated with the laser, therebyreducing the amount of the laser power that actually strikes the surfaceof the optical disc. Also, the laser itself may suffer degradation inperformance over time, further reducing the laser power. As aconsequence, the label writing capability of the optical disc drive maybe significantly degraded over time.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention can be understood with reference to the followingdrawings. The components in the drawings are not necessarily to scale.Also, in the drawings, like reference numerals designate correspondingparts throughout the several views.

FIG. 1 is a block diagram of an optical disc drive that employs laserpower calibration according to an embodiment of the present invention;

FIG. 2 is a drawing of an optical disc to which a calibration pattern iswritten in the optical disc drive of FIG. 1 according to an embodimentof the present invention;

FIG. 3 is a graph that depicts a reliable range of reflectivity sensedfrom segments on an optical disc in the optical disc drive of FIG. 1according to an embodiment of the present invention;

FIG. 4 is a flow chart of an embodiment of a laser power calibrationsystem employed in the optical disc drive of FIG. 1 according to anembodiment of the present invention;

FIG. 5 is a flow chart of an additional embodiment of a laser powercalibration system employed in the optical disc drive of FIG. 1according to an embodiment of the present invention;

FIG. 6 is a flow chart of an additional embodiment of a laser powercalibration system employed in the optical disc drive of FIG. 1according to an embodiment of the present invention;

FIG. 7 is a graph that depicts a darkness generated in a segment as afunction of a power of a laser in the optical disc drive of FIG. 1according to an embodiment of the present invention;

FIG. 8 is a flow chart of an additional embodiment of a laser powercalibration system employed in the optical disc drive of FIG. 1according to an embodiment of the present invention;

FIG. 9 is a graph that depicts the reflectivity of an optical disc as afunction of the voltage of a sensor employed in the optical disc driveof FIG. 1 according to an embodiment of the present invention;

FIG. 10 is a flow chart of an additional embodiment of a laser powercalibration system employed in the optical disc drive of FIG. 1according to an embodiment of the present invention; and

FIG. 11 is a flow chart of an additional embodiment of a laser powercalibration system employed in the optical disc drive of FIG. 1according to an embodiment of the present invention.

DETAILED DESCRIPTION

With reference to FIG. 1, shown is an optical disc drive 100 accordingto an embodiment of the present invention. The optical disc drive 100 isin data communication with a host 103. In this respect, the host 103 maybe, for example, a computer system, server, or other similar device. Forthe purposes of the following discussion, first the structural aspectsof the optical disc drive 100 are discussed. Thereafter, the operationof the optical disc drive 100 is discussed with respect to thecalibration of a laser power setting according to the variousembodiments of the present invention.

In one embodiment, the optical disc drive 100 includes a processorcircuit 106. The processor circuit comprises a processor 113 and amemory 116, both of which are coupled to a local interface 119. In thisrespect, the local interface 119 may be, for example, a data bus with anaccompanying control/address bus as can be appreciated by those withordinary skill in the art. The optical disc drive 100 further includesan optical pickup unit 123, an actuator 126, a spindle 129, and apositional sensor 133. When in use, an optical disc 136 is placed on thespindle 129 as shown. The optical pickup unit 123, actuator 126, spindle129, and positional sensor 133 are all operatively or electricallycoupled to the processor circuit 106. In particular, these componentsare coupled to the processor circuit 106 by way of an electricalconnection through which electrical signals may be received from ortransmitted by the processor circuit 106 in orchestrating the operationof the optical disc drive 100 as will be described. In oneimplementation, the optical pickup unit 123, actuator 126, spindle 129,and the positional sensor 133 are coupled to the local interface 119through appropriate interface circuitry (not shown) as can beappreciated.

The actuator 126 may comprise, for example, a stepper motor or othersuch device. The actuator is operatively coupled to the optical pickupunit 123, for example, using a screw shaft 139. In this respect, theactuator 126 may be manipulated by the processor circuit 106 in order tomove the optical pickup unit 123 back and forth along the length of thescrew shaft 139 during the normal operation of the optical disc drive100 as will be described. In this respect, the actuator 126 positionsthe optical pickup unit 123 relative to the optical disc 136 during thenormal course of operation of the optical disc drive 100.

The optical pickup unit 123 includes a laser 140 and a sensor 141 thatmay be employed to read data from the optical disc 136. In this respect,the laser 140 is controlled to generate laser light 142 that is directedto the optical disc 136. The laser 140 may operate at any one of anumber of frequencies as can be appreciated by those with ordinary skillin the art. At least a portion of the laser light 142 may reflect off ofthe optical disc as reflected laser light 143. Data structures areembodied in the optical disc 136 that reflect the laser light 142 as canbe appreciated by those with ordinary skill in the art. One or moreoptical components such as a lens may be employed in the optical pickupunit 123 to focus the laser light 142 generated by the laser 140 or tofocus the reflected laser light 143 as can be appreciated.

The sensor 141 detects reflected laser light 143 during a read operationand generates a voltage signal that is applied to the processor circuit106. The magnitude of the voltage signal generated by the sensor 141 isgenerally proportional to the magnitude of the incident reflected laserlight 143 that falls upon the sensing surface area of the sensor 141.Alternatively, a current signal may be generated by the sensor 141. Thesensor 141 may be a single sensor or multiple sensors operatingcooperatively. Where multiple sensors are employed as the sensor 141,the voltage signal may be a sum of all of the voltage signals from eachof the multiple sensors. Such a signal may be referred to as a “sumsignal”.

The optical pickup unit 123 may be manipulated to write data to theoptical disc 136 by controlling the laser 140 in the optical pickup unit123 so as to form the data structures in the optical disc. The writingcapabilities of the optical disc drive 100 may also be employed to writea label on a label surface of the optical disc 136. Specifically, thelabel surface of the optical disc 136 is chemically treated so as tochange an optical property such as darkness, reflectivity, or color uponbeing irradiated with laser light from the optical pickup unit 123. Suchtreatment includes, for example, a coating of thermo-chromic materialthat has been screen-printed on the label surface such that thismaterial changes from light to dark color when activated by the laser.The thermo-chromic material may comprise, for example, a mixture ofcolor-forming dye, activator, and infrared antenna contained in apolymer matrix. The infrared antenna absorbs the laser energy andconverts it to heat. The heat causes the activator, dye, and the polymermatrix to melt, thereby allowing the activator to interact with the dye.The interaction results in a chemical change to the dye that causes achange in color. The label material may vary slightly from manufacturerto manufacturer, or from one disc to another disc, or even from oneregion on a disc to another region on the same disc. As a consequence,the appearance of the generated label may vary accordingly.

The spindle 129 comprises a motor or other such device that spins theoptical disc 136. This motor may be, for example, a stepper motor orother type of motor. In this respect, the optical disc 136 is placed ina seating position relative to the spindle 129. Thereafter, the opticaldisc 136 may be spun relative to the optical pickup unit 123 and thepositional sensor 133. The positional sensor 133 obtains positional data146 from the optical disc 136 as it rotates on the spindle 129. Byvirtue of the positional data 146 obtained, the precise location of theoptical pickup unit 123 relative to the optical disc 136 can be trackedduring calibration of the laser power setting and during writing of alabel to the optical disc 136.

The optical disc drive 100 further comprises a number of componentsstored in the memory 116 and executable by the processor 113 in order tocontrol the operation of the various components of the optical discdrive 100. These components comprise, for example, an operating system153 and a disc drive controller 156. The disc drive controller 156 isexecuted by the processor 113 to control the various operations of theoptical disc drive 100. In this respect, the disc drive controller 156orchestrates the general operation of the optical disc drive 100 inwriting data to and reading data from optical discs 136. The disc drivecontroller 156 also orchestrates the operation of the optical disc drive100 in writing a label on a surface of an optical disc 136.

The disc drive controller 156 includes a laser power calibration system159. The laser power calibration system 159 is executed as a portion ofthe disc drive controller 156 to calibrate the power of the laser 140 inthe optical pickup unit 123 to optimize the writing of a label to thesurface of the optical disc 136 as will be discussed. In one embodiment,the optical pickup unit 123 is coupled to the local interface 119 withan interface circuit that includes a register that holds a digital valuethat controls the power of the laser 140. In one embodiment, the digitalvalue is converted to an analog voltage that drives the laser 140 anddetermines the power of the laser beam 140 generated thereby. In thisrespect, the value written to the register in such an interface circuitrepresents a laser power setting. To adjust or change the power of thelaser 140, the laser power setting is correspondingly altered by writinga new value to the register as can be appreciated. Alternatively, thepower of the laser 140 may be controlled in some other manner as can beappreciated. The laser power calibration system 159 employs one or morecalibration patterns 166 that are written to the surface of the opticaldisc 136 during the calibration of the laser power setting as will bedescribed.

Where embodied in the form of software or firmware, the disc drivecontroller 156 and the laser power calibration system 159 may beimplemented using any one of a number of programming languages such as,for example, C, C++, Assembly, or other programming languages. The discdrive controller 156 as may be implemented, for example, in an objectoriented design or in some other programming architecture. Where anyportion of the disc drive controller 156 and/or the laser powercalibration system 159 is represented in a flow chart herein, assumingthat the functionality depicted is implemented in an object orienteddesign, for example, then each block of such flow charts may representfunctionality that is implemented in one or more methods that areencapsulated in one or more objects.

The memory 116 may comprise, for example, random access memory (RAM),such as, for example, static random access memory (SRAM), dynamic randomaccess memory (DRAM), or magnetic random access memory (MRAM) and othersuch devices. In addition, the memory 116 may also include, for example,read-only memory (ROM) such as a programmable read-only memory (PROM),an erasable programmable read-only memory (EPROM), an electricallyerasable programmable read-only memory (EEPROM), or other like memorydevice.

In addition, the processor 113 may represent multiple processors and thememory 116 may represent multiple memories that operate in parallel. Insuch a case, the local interface 119 may be an appropriate network thatfacilitates communication between any two of the multiple processors,between any processor and any one of the memories, or between any two ofthe memories etc. The processor 113 may be of electrical, optical, ormolecular construction, or of some other construction as can beappreciated by those with ordinary skill in the art.

The operating system 153 is executed to control the allocation and usageof hardware resources such as the memory, processing time and peripheraldevices in the optical disc drive 100. In this manner, the operatingsystem 153 serves as the foundation on which applications depend as isgenerally known by those with ordinary skill in the art.

Next, the general operation of the optical disc drive 100 in writing alabel to an optical disc 136 is described according to an embodiment ofthe present invention. The disc drive controller 156 controls theoperation of the various components of the optical disc drive 100 inorder to write a label onto the surface of the optical disc 136. Thedisc drive controller 156 also controls the operation of the variouscomponents of the optical disc drive 100 when writing data to andreading data from the optical disc 136. However, discussion of thewriting and reading tasks are not described herein in detail.

To the extent that the disc drive controller 156 orchestrates theoperation of the various components of the optical disc drive 100 inorder to write a label onto the surface of the optical disc 136, itcontrols the movement of the optical pickup unit 123 by manipulating theactuator 126 to cause the optical pickup unit 123 to move along thescrew shaft as needed. In addition, the disc drive controller 156controls the rotation of the optical disc 136 by controlling the speedof the spindle 129. Also, the disc drive controller 156 can control theread and write functions of the optical disc drive 100 by manipulatingthe optical pickup unit 123 to transmit laser light 142 to the disc.When the optical pickup unit 123 reads data from the disc, then thereflected laser light 143 is sensed by the sensor 141 and acorresponding signal is generated that is applied to the processorcircuit 106 through an appropriate interface circuit.

In addition, the disc drive controller 156 causes the optical pickupunit 123 to focus the laser 142 as it is directed at the optical disc136. In this respect, the focusing function may be performedcontinuously while the optical disc 136 spins and the laser 142 isdirected thereto during the performance of label writing functions, orother operations.

The disc drive controller 156 also tracks the position of the opticaldisc 136 based upon inputs from the positional sensor 133. Inparticular, the positional sensor 133 senses the passing of spokes 146disposed on the optical disc 136 near, for example, the center, althoughthe spokes may be located at some other position on the optical disc136. Each time a spoke 146 passes the positional sensor 133, thepositional sensor 133 generates a pulse that is received by the discdrive controller 156 by way of the local interface 119. In this respect,each pulse may be viewed as a signal or an interrupt that informs thedisc drive controller 156 of a component rotation of the optical disc136. To track the actual location of the optical disc 136 based upon thepulses, the disc drive controller 156 may include a counter that countsthe pulses up to a total number of pulses in a single rotation todetermine the actual position of the optical disc 136 at a given time.

Thus, the location of the laser beam generated by the optical pickupunit 123 relative to the optical disc 136 may be determined at any giventime by virtue of the positional data tracked by the disc drivecontroller 156 based upon the data generated by the positional sensor133. In particular, the location of the optical pickup unit 123 relativeto a predefined position on the optical disc 136 of each pixel orsegment of a label that is to be written to the optical disc 136 may becalculated based upon the relative positions of each of the spokes 146sensed by the positional sensor 133.

By virtue of the above-mentioned components, the disc label controller153 orchestrates the writing of a label on a surface of the optical disc136. In this respect, the label to be written to the circular opticaldisc 136 may be embodied in the form of radial data that comprises anumber of concentric and adjacent circular tracks, or that comprises aspiral.

When writing the label in the form of circular tracks to the opticaldisc 136, each track is received from the host 103 and temporarilystored in the memory 116. In some embodiments, the memory 116 may not belarge enough to accommodate all of the tracks of the label that iswritten to the surface of the optical disc 136. Consequently, the host103 transmits the tracks to the optical disc drive 100 for temporarystorage in the memory 116. The rate at which the tracks are transmittedis typically chosen so as to maintain a minimum number of tracks in thememory 116 at all times during a label writing operation so that theappropriate number of tracks are always present within the memory 116when they are needed for labeling the optical disc 136.

To properly write a label to the label surface of the disc 136, thelaser power setting is specified so that power of the laser 140 resultsin the desired marking of the various pixels that make up the label. Ifthe power of the laser 140 is too low, then the marks on the respectivepixels will be too light and the quality of the resulting label would bediminished. Also, such light marks tend to fade over time, furtherreducing the quality of the label.

On the other hand, if the power of the laser 140 is too high, then thetemperature of the coating on the label surface becomes too high. As aresult, the coating tends to sputter and may leave deposits on a lensassociated with the optical pickup unit 123. This is called “ablation”.Ablation of the coating on the label surface that leaves deposits onlenses associated with the optical pickup unit 123 can degrade the labelwriting performance of the optical disc drive 100 over time. Note that aparticular pixel may be written to multiple times, provided that thereis adequate cooling between writes so that the ultimate temperature ofthe coating never reaches a point where sputtering occurs over thecourse of multiple writes.

Thus it is desirable to set the laser power such that the darkestpossible marks on pixels can be made without causing ablation. Whenoptical disc drives 100 are manufactured at the factory, the laser powersetting may be optimized for the best performance. However, when theoptical disc drive 100 is used over time, degradation inevitably occurs.Specifically, dust and other particles generally collect on the lensthat focuses the laser 140, thereby reducing the power of the laser thatactually strikes the label surface of the optical disc 136. Also, thelaser 140 itself my suffer degradation in performance over time, furtherreducing the laser power. As a consequence, the label writing capabilityof the optical disc drive 100 may be significantly degraded over time.

In order to address the problem of degradation in the ability of theoptical disc drive 100 to write labels to the label surface of opticaldiscs over time, in various embodiments, the present invention providesfor the calibration of the power of the laser 140. Specifically, variousembodiments of the laser power calibration system 159 are described thatprovide for the calibration of the laser power on an ongoing basis overtime. Each embodiment of the laser power calibration system 159 isdiscussed with reference to the figures that follow.

With reference to FIG. 2, shown is a drawing of an optical disc 136 witha calibration pattern 166 written, for example, on a track 169 of theoptical disc 136. The calibration pattern 166 comprises, for example, arepeated pattern of segments 173 written thereto. For all of theembodiments described herein, the size of the segments 173 may vary asis appropriate. For example, in one embodiment, the segments 173 may bethe size of a single pixel, for example, of a label to be written to thelabel surface of the optical disc 136. Alternatively, each segment 173may be the size of two or more adjacent pixels of the label. In writinga calibration pattern 166 to the optical disc 136, the laser powercalibration system 159 (FIG. 1) activates the laser 140 (FIG. 1) atpredefined laser power settings for each segment 173 to deliver adesired quantum of radiant energy in the form of laser radiation to thelabel surface of the optical disc 136. When the laser 140 is activatedfor a specific segment 173, the segment 173 is deemed to be a “markedsegment”. Until the laser 140 is activated for respective segments 173,then they are deemed to be “unmarked segments”.

The darkness of a marked segment 173 depends upon the quantum of radiantenergy that is delivered to the label surface at the location of themarked segment 173 by the laser 140. The total amount of radiant energydelivered to a given segment depends upon the “dwell” time of the laser140 with respect to the given segment which, in turn, depends upon therotational speed of the spindle 129 (FIG. 1) and the power of the laser140. Where the rotation speed of the spindle does not change, then thepower of the laser 140 is adjusted by altering the laser power settingto deliver more or less radiant energy to the label surface at thelocation of the respective segments 173.

The calibration patterns 166 may vary significantly, depending upon theparticular laser power calibration approach employed as will bedescribed. For example, the calibration pattern 166 may comprisecreating a plurality of repeated arrays of marked segments 173. Eacharray of marked segments 173 is created using multiple different laserpower settings applied to the laser 140. In this respect, each array ofmarked segments 173 is created with multiple different quanta of radiantenergy from the laser 140. Thus, each marked segment 173 in such anarray is created using a quantum of radiant energy from the laser 140that differs from the quantum of radiant energy applied to the remainingmarked segments 173 in the array. Such an array may include, forexample, marked segments that present a spectrum of darkness, from verylight to very dark marked segments 173.

Alternatively, the calibration pattern 166 may comprise marking all ofthe segments 173 with a single laser power setting, thereby creatingmultiple marked segments of relatively uniform darkness. In addition,the same calibration pattern 166 may be written over the same segmentsmultiple times. In this respect, each of the marked segments 173 may bewritten to multiple times using the laser 140. Each time a respectivesegment is written to by the laser 140, it becomes darker and darker asthe total quantum of radiant energy applied to the marked segmentcomprises an aggregate of the radiant energy from the repeatedapplication of the laser 140.

In another alternative, the calibration pattern 166 may comprise a“stitch” pattern that includes both marked and unmarked segments 173. Inone embodiment, the marked and unmarked segments 173 comprise pairs thatare in relative proximity to each other on the optical disc 136. Byvirtue of the stitch pattern, it may be possible to ascertain thedifference in reflectivity between the marked and unmarked segments 173as will be discussed.

Even though one or perhaps more tracks on the optical disc 136 may bemarked with a given calibration pattern 166 during calibration of thelaser power, the calibration pattern 166 will not degrade or otherwisemar the label to be written to the label surface of the optical disc136. This is because a single track on the optical disc 136 is typicallyonly a few microns in width and a calibration pattern 166 written to asingle track would not be wide enough to be perceived by the naked eye.In addition, in one embodiment the calibration pattern 166 is written tothe innermost or outermost portion or track of the optical disc 136 tominimize interference with the label to be written in the remainingportion of the optical disc 136. As an additional alternative, thecalibration pattern 166 may be written on any track on the optical disc136. In still an additional alternative, the calibration pattern 166 maybe written over segments that are to be marked as part of the label thatis written to the label surface of the disc 136.

Once a calibration pattern 166 has been written to the label surface ofthe optical disc 136, then a reading of the reflectivity of the markedsegments 173 of the calibration pattern 166 may be taken. This is doneby positioning the optical pickup unit 123 (FIG. 1) over the markedsegments 173 such that the sensor 141 receives any reflected laser light143 (FIG. 1) from the respective marked segment 173. Thereafter, thelaser power setting is set at a low setting that results in laserradiation of diminished power that is not powerful enough to impartenough radiant energy resulting in further darkening of the respectivemarked segment 173. Such a low laser power setting is defined herein asa “reflectivity read” setting. In one embodiment, the reflectivity readsetting comprises setting a laser power of 5 mW, although other lowpower settings may be employed. Once the laser 140 is activated at thereflectivity read setting, an amount of reflected laser light 143 isdetected by the sensor 141. The amount of reflected laser light 143detected depends upon the darkness of the respective marked segment 173for which the reflectivity is measured.

With these concepts in mind, reference is made to FIG. 3 that depicts agraph of the reflectivity sensed from marked segments 173 as a functionof the laser power setting. In particular, the laser power settingsdepicted are those that deliver the quantum of radiant energy needed tomark a segment 173 resulting in the darkness that, in turn, results inthe corresponding reflectivity depicted in the graph. The actual quantumof radiant energy may be delivered in a single laser write cycle or overthe course of repeated laser write cycles to a given segment 173.

As shown, the reflectivity is relatively flat and high when the laserpower setting is relatively low up to a “knee” 183 in the curve.Thereafter, the reflectivity drops with increasing laser power. Thereflectivity of segments marked with laser power settings to the left ofthe knee 183 generally reflect the fact that no perceivable mark is madeon segments at such power levels. After the knee, the reflectivity dropsin an approximate linear manner until an “ankle” 186 is reached. Theankle 186 represents a point where the measured reflectivity begins tolevel off in spite of the fact that the laser power setting increases.To the right of the ankle 186, although the curve appear flat in FIG. 3,the reflectivity readings may be unreliable to the right of the ankle186 and may fluctuate. Also, the reflectivity readings to the right ofthe ankle 186 may vary due to the onset of possible ablation and otherdamage to the label surface. However, even though readings of thereflectivity may be unreliable to the right of the ankle 186, it ispossible with some label chemistries that the segments will continue tobecome darker with increasing laser power settings to the right of theankle 186. The exact behavior with respect to darkening at laser powersettings extending to the right of the ankle 186 may be determinedempirically. Thus, a region of reliable reflectivity 189 exists betweenthe knee 183 and the ankle 186 in which the reflectivity varies as afunction of the laser power setting. The reflectivity within the regionof reliable reflectivity 189 ranges from a low reflectivity R_(L) to ahigh reflectivity R_(H).

In the following discussion, various embodiments are provided in which alaser power of the laser 140 is calibrated in the optical disc drive 100(FIG. 1). In the various embodiments described, a plurality of markedsegments 173 of a calibration pattern 166 are written onto a labelsurface of an optical disc 136 with the laser 140. In this respect, themarked segments 173 are created by the application of assorted quanta ofradiant energy from the laser 140 (FIG. 1), depending upon thecalibration pattern 166 employed as described above. In this respect,the quantum of radiant energy applied to create each marked segment maybe from a single application of the laser 140 or may be from multipleapplications of the laser 140 as described above.

The reflectivity of the marked segments 173 created with each quantum ofradiant energy is measured by taking readings from the sensor 141 in theoptical pickup unit 123. Based upon the measured reflectivities of themarked segments for each quantum of radiant energy, the power of thelaser 140 is set for writing a label.

Referring next to FIG. 4, shown is a flow chart that provides oneexample of the operation of the laser power calibration system 159,denoted herein as laser power calibration system 159 a, according to anembodiment of the present invention. Alternatively, the flow chart ofFIG. 4 may be viewed as depicting steps of an example of a methodimplemented in the optical disc drive 100 (FIG. 1) to calibrate thepower of the laser 140 (FIG. 1) for use in writing a label to the labelsurface of the optical disc 136 (FIG. 1).

Beginning with box 201, the laser power calibration system 159 ameasures and stores the reflectivity of unmarked segments that will bemarked as part of the calibration pattern 166 (FIG. 2). In this respect,a reflectivity of each of the segments 173 is obtained before they havebeen written to by the laser 140. This is done, for example, with thelaser power setting at the reflectivity read setting. By obtaining areading of the reflectivity of the unmarked segments as such, an amountof noise resulting from process variation in the coating of the labelsurface that affects the reading of the reflectivity of pixels isdetermined. Then, box 203, the laser power calibration system 159 aimplements a writing of a calibration pattern 166 (FIG. 2) on theunmarked portion of the optical disc 136 (FIG. 1) that was measured inbox 201. In this respect, the calibration pattern 166 may be written ona designated track 169 (FIG. 2) as described above. Alternatively, thecalibration pattern 166 may be written onto segments 173 (FIG. 2) thatare to be marked during the course of writing the label onto the labelsurface of the disc 136. The calibration pattern 166 written to theoptical disc 136 comprises the number of arrays of marked segments 173,where each array of marked segments 173 includes segments created withmultiple different quanta of radiant energy from the laser 140. In thisrespect, the array of marked segments 173 may comprise a number ofsegments 173 that are marked with the laser 140 set at successivelygreater laser power settings for a given rotational speed, therebydelivering successively greater quanta of radiant energy to each segment173 in the array. Stated another way, the marked segments 173 of thearray are written with successively higher laser power settings from thefirst marked segment 173 to the last marked segment 173 in the array.For example, the array may comprise ten different marked segments 173,each segment being marked with the laser 140 set at one of ten differentlaser power settings. Such an array may be viewed as a “stair step”configuration of marked segments 173.

In one embodiment, the array of marked segments 173 is repeated on agiven track of the optical disc 136 multiple times to provide for anumber of reflectivities for each laser power setting or quantum ofradiated energy delivered to the respective marked segments 173 so thatan average reflectivity for each laser power setting/quantum of radiatedenergy may be calculated.

Next, in box 206, the laser power calibration system 159 a implements ameasuring, adjustment, and storing of the reflectivity of each of themarked segments 173 of the respective calibration pattern 166 written tothe optical disc 136. To adjust the reflectivity readings obtained, thereflectivities measured in box 201 are subtracted from the correspondingreflectivities measured in box 206. In this respect, the measurements ofthe reflectivity obtained in box 206 are adjusted for noise created dueto the process variation in the coating on the label surface on theoptical disc 136. Thereafter, in box 209, the average reflectivitiesassociated with each respective quanta of radiant energy or with eachlaser power setting are calculated from the reflectivity of therespective marked segments 173 as obtained in box 206 above.Alternatively, rather than obtaining an average reflectivity for eachquanta of radiant energy, a select reflectivity measured and adjustedfrom one of the marked segments 173 in box 206 for each quanta ofradiant energy may be employed. In such a situation, box 209 may beomitted.

In addition, even though the various embodiments of the presentinvention discussed herein are described as employing averagereflectivities for the various purposes noted, in general it isunderstood that non-averaged reflectivity measurements may be employeddirectly for the various purposes described. In such case, any steps,logic, or code specified to determine an average reflectivity in thevarious embodiments described herein may be omitted as appropriate.

Next, in box 213, the average reflectivities associated with the lowesttwo consecutive laser power settings or quanta of radiant energy areidentified for further analysis. In this respect, the marked segments173 were thus written with a range of laser power settings, thusresulting in a range of quanta of radiant energy applied to the variousmarked segments 173 as described above.

Next, in box 216, a differential in the average reflectivity between thetwo reflectivities identified in box 213 is calculated. Given that thelowest two reflectivities are likely to be to the left of or otherwisenear the knee 183 (FIG. 3) of the curve described above with referenceto FIG. 3, it is unlikely that the differential between the two averagereflectivities will be very large. Thus, in box 219, the laser powercalibration system 159 a determines whether the average reflectivitiesfall to the right or the left of the knee 183 in the reflectivity curveof FIG. 3. This may be determined, for example, by ascertaining whetherthe differential between the two current consecutive reflectivities isgreater than a predefined threshold indicating that the reflectivitiesfall to the left of the knee 183 where a greater slope exists.

If the average reflectivities fall to the left of the knee 183 asidentified in box 219, then the laser power calibration system 159 aproceeds to box 223. Otherwise, the laser power calibration system 159 aprogresses to box 226.

Assuming that the laser power calibration system 159 a has proceeded tobox 223, then the average reflectivities of the next consecutive twopower settings, including the highest of the previous consecutive powersettings, are identified for further analysis. Thereafter, the laserpower calibration system 159 a reverts to box 219 as shown. Thus, thelaser power calibration system 159 a remains in a loop in boxes 219 and223 until the average reflectivities indicate that a laser power settinghas been reached, where the quantum of radiant energy delivered is suchthat the resulting reflectivities fall to the right of the knee 183inside of the region of reliable reflectivity 189 (FIG. 3). In thisrespect, the laser power settings corresponding to the location of theknee 183 are identified.

Given that the reflectivities measured to the right of the knee 183 fallwithin the region of reliable reflectivity 189, then an appreciabledifferential should exist between the reflectivity readings taken forconsecutive laser power settings. Once the laser power settings aresufficiently high that the ankle 186 has been reached, then thereflectivity difference between two consecutive average reflectivitiesshould diminish given that the drop in the reflectivity no longer occursas was the case within the region of reliable reflectivity 189. This isbecause the reflectivity to the right of the ankle 186 is somewhatunpredictable, but is generally flat relative to the slope of thereflectivity in the region of reliable reflectivity 189.

Thus, in box 226, the laser power calibration system 159 a calculatesthe average reflectivity differential between the reflectivitiesassociated with the next two consecutive power settings that include theone of the reflectivities of the previous highest laser power setting.Thereafter, in box 229, the laser power calibration system 159 adetermines whether the ankle 186 (FIG. 3) has been detected due to thefact that the differential is less than a predefined threshold asdescribed above. If such is the case, then the laser power calibrationsystem 159 a proceeds to box 233. Otherwise, the laser power calibrationsystem 159 a reverts back to box 226 as shown. Thus, in boxes 226 and229 are repeatedly performed in a loop until the laser power calibrationsystem 159 a detects the ankle 186 as described.

Assuming that the ankle 186 has been detected in box 229, then in box233 the laser power setting of laser 140 is set at an optimal lasersetting relative to the laser power settings associated with thelocation of the knee 183 and the ankle 186 that results in a maximumdarkness for marked segments without ablation or sputtering. For somelabel chemistries, the optimal laser power setting may be the lower ofthe current two consecutive power settings for which the last averagereflectivity differential was calculated in box 226. Alternatively, thelaser power setting may be set at a value that is a predefined intervalto the right of the ankle 186. This interval may be a predefined offset,for example, or a predefined percentage of the difference of the laserpower setting between the ankle 186 and the knee 183. Also, for stillother label chemistries, the optimal laser power setting may be locatedat some predefined point between the knee 183 and the ankle 186. Theprecise location of the optimal laser power setting relative to thelocations of the knee 183 and/or the ankle 186 may be determinedempirically for each label chemistry. The ultimate optimal laser powersetting is then used for writing segments of a label to the labelsurface of the optical disc 136 as the maximum darkness for the segmentswritten is achieved without ablation or sputtering as was describedabove.

In an additional embodiment, once the laser power setting is identifiedin box 233, the laser power settings for those segments in each arraythat generated a reflectivity in the region of reliable reflectivity 189may be employed to generate various levels of darkness that fall on agrey scale to provide for a greater range of darkness to be employed inwriting the ultimate image to the label surface of the optical disc. Inparticular, in writing the label to the label surface, the laser powersettings may be employed to generate segments of varying darkness,depending upon the desired shade of grey needed in the image.

In addition, it may be the case that noise occurs in the reflectivitysensed from the segments marked as part of the calibration pattern 166.Consequently, the interval between any two laser power settings isspecified so as to ensure that average reflectivity differentialscalculated are not compromised by the level of the noise.

Referring next to FIG. 5, shown is a flow chart that provides anotherexample of the operation of the laser power calibration system 159,denoted herein as laser power calibration system 159 b, according to anembodiment of the present invention. Alternatively, the flow chart ofFIG. 5 may be viewed as depicting steps of an example of a methodimplemented in the optical disc drive 100 (FIG. 1) to calibrate thepower of the laser 140 (FIG. 1) for use in writing a label to the labelsurface of the optical disc 136 (FIG. 1). The flow chart of FIG. 5illustrates an approach to calibrate the power of the laser 140 thatcompares reflectivity differentials obtained from various measurementsof the reflectivities at measured arrays of predefined laser powersettings.

Beginning with box 250, the laser power calibration system 159 bmeasures and stores the reflectivity of unmarked segments that will bemarked as part of the calibration pattern 166 (FIG. 2). In this respect,a reflectivity of each of the segments 173 is obtained before they havebeen written to by the laser 140. Next, in box 253, the averagereflectivity is calculated from the reflectivities of each of theindividual unmarked segments 173. Thereafter, in box 256, the laserpower calibration system 159 b writes the calibration pattern 166 to theoptical disc 136 (FIG. 1). In this respect, the calibration pattern 166comprises, for example, a number of repeated arrays of segments, wherethe laser power settings vary within each array across a predefinedrange of laser power settings. In one embodiment, the range of laserpower settings is less than a total operating range of the laser 140.

For example, assume that the laser power setting has an operating rangefrom 0 to 40 milliwatts. The range of the laser power settings of thearray may be, for example, 10 to 20 percent of the total operatingrange. For example, if the range of laser power settings of the arraycovered a range that was 20% of the operating range from 0 to 40milliwatts (mW), then the range of laser power settings may be 0 to 8mW. In this respect, the range of laser power settings is a subset orwindow within the total operating range of the laser 140. The range orwindow of 8 mW, for example, may be shifted up and down the operatingrange of the laser 140 in order to detect the knee 183 and ankle 186 aswill be described. In this respect, the range or window may be, forexample, 0 to 8 mW, 30-38 mW, or other window within the operating rangeof 0 to 40 mW. The array comprises a plurality of specific laser powersettings. For example, assuming that the array fell between 0 and 8 mW,and assuming a resolution of 10 total laser power settings, the specificlaser power settings may be, for example, 0.8 mW, 1.6 mW, 2.4 mW, 3.2mW, and so on.

Alternatively, the calibration pattern 166 may be written over aplurality of marked segments that comprise pixels of an image that is tobe written to the surface of the optical disc 136. In this respect, nosegments 173 are marked solely for the purposes of calibration, whereultimately the only marked segments appearing on the optical disc 136comprise the pixels of the image itself after the image is created.However, to the extent that the segments marked for purposes ofcalibration are not perceivable to the naked eye, any segments markedfor calibration that are not part of the ultimate image may be of littleconsequence to the resulting image.

Next, in box 259, the reflectivity of each of the marked segments 173 ofthe current repeated array written to the optical disc 136 is measuredand stored in the memory 116 (FIG. 1). Then, in box 263, an averagereflectivity is calculated for each laser power setting in the arrayapplied to the optical disc 136 from the reflectivities of each of theindividual marked segments 173 of the arrays written as part of thecalibration pattern. Thereafter, in box 266, for each of the laser powersettings of the repeated array written to the optical disc 136 as thecalibration pattern, a first average reflectivity differential iscalculated between the respective average reflectivities calculated inbox 263 and the average reflectivity calculated in box 253 above. Thefirst average reflectivity differentials may be calculated, for example,by subtracting the average reflectivities calculated in box 263 for eachlaser power setting in the repeated array from the average reflectivityof the unmarked segments calculated in box 253 above.

Thereafter, in box 269, the calibration pattern 166 is rewritten overthe marked segments 173 that were measured as set forth in box 250 andpreviously marked as set forth in box 256 above. To ensure thatsputtering or ablation does not occur, the rewriting of the calibrationpattern 166 in box 269 is performed after the marked segments havecooled sufficiently after the writing of the calibration pattern 166 inbox 259 above. By rewriting the calibration pattern 166 over the samemarked segments 173, the reflectivity of each respective marked segmentshould decrease accordingly as the ultimate quantum of radiant energyapplied to such segments 173 has doubled, thereby darkening the markedsegments.

Next, in box 273, the reflectivity of the marked segments 173 ismeasured a second time and stored in the memory 116. Thereafter, in box276, a second average reflectivity is calculated for each laser powersetting in the repeated array of the calibration pattern from thereflectivities of each of the respective marked segments 173. Then, inbox 279, for each of the laser power settings of the repeated arraywritten to the optical disc 136 as the calibration pattern, a secondaverage reflectivity differential is calculated. This is determined bysubtracting the first respective average reflectivities calculated inbox 263 after the calibration pattern 166 is first written to the disc136 from the corresponding second average reflectivities calculated inbox 276 after the calibration pattern 166 is written to the optical disc136 a second time.

In box 283, the laser power calibration system 159 b determines whetherthe knee 183 (FIG. 3) in the reflectivity curve has already beendetected. If not, then the laser power calibration system 159 b proceedsto box 286. Otherwise, the laser power calibration system 159 bprogresses to box 289.

In box 286, the laser power calibration system 159 b attempts to detectthe laser power setting that coincides with, or is centered at the knee183. This may be accomplished, for example, by examining the first andsecond average reflectivity differentials for each laser power settingwritten to the optical disc 136. Specifically, the first and secondaverage reflectivity differentials are both relatively small andapproximately equal when the reflectivities measured in boxes 259 and273 fall to the left of the knee 183 as no appreciable mark has beenmade on the respective segments. The first and second averagereflectivity differentials may both be relatively large andapproximately equal when the reflectivities measured in boxes 259 and273 fall between the knee 183 and the ankle 186. Also, the first andsecond average reflectivity differentials are both relatively small andapproximately equal when the reflectivities measured in boxes 259 and273 fall to the right of the ankle 186. The first and second averagereflectivity differentials differ when the reflectivities measured inboxes 259 and 273 approach either the knee 183 or the ankle 186. Withthe foregoing in mind, the laser power calibration system 159 b may beconfigured to detect the location of the knee 183 and the ankle 186based upon the first and second average reflectivity differentials.Alternatively, in another embodiment, the value of the second averagereflectivity differential may be employed to find the knee 183 and theankle 186.

If in box 286, the laser power calibration system 159 b does not detectthe knee 183, then the laser power calibration system 159 proceeds tobox 293. Otherwise, the laser power calibration system moves to box 296.In box 293, the range of the laser power settings of the repeated arraywritten to the optical disc 136 as the calibration pattern is shifted tothe right by increasing an offset associated with the range. Forexample, if the range was from 0 to 8 mW, it may be shifted by anincrement of 1 mW to a range of 1 to 9 mW. According to one embodiment,the offset may be any magnitude, but is typically less than the rangeitself (i.e. 8 mW) and is not specified so as to move beyond theoperating range of the laser 140. Next, the laser power calibrationsystem 159 b reverts back to box 250 to begin the process once more withthe new range of laser power settings for the repeated array. In thisrespect, the calibration patterns written once more in boxes 256 and 269are written over a new set of unmarked segments 173 that may or may notbe on a new track, etc.

Assuming that the knee 183 has been detected in box 286, then in box296, the laser power setting associated with the knee 183 is stored forfuture use. Thereafter, the laser power calibration system 159 bproceeds to box 289.

Assuming that the laser power calibration system 159 b has proceeded tobox 289, then the laser power calibration system 159 b determineswhether the ankle 186 can be detected using the first and second averagedifferentials as described above. If so, then the laser powercalibration system 159 b proceeds to box 299. Otherwise, the laser powercalibration system 159 b reverts to box 293. In this respect, the laserpower calibration system 159 b starts with an initial array of laserpower settings and, with each cycle of the loop described, the array oflaser power settings is shifted over to the right until the knee 183 andthe ankle 186 are discovered.

If the ankle 186 is detected as described above in box 289, then in box299 the laser power setting is set to an optimum laser power settingthat would deliver the quantum of radiant energy from the laser 140 thatresults in the first average reflectivity. Thereafter, the power of thelaser 140 is thus calibrated for operation to write a label to theoptical disc 136. The optimum laser power setting is determined, forexample, based upon the laser power setting at the ankle 186 and thelaser power setting at the knee 183 as described above with reference tobox 233 (FIG. 4).

Referring next to FIG. 6, shown is a flow chart that provides oneexample of the operation of the laser power calibration system 159,denoted herein as laser power calibration system 159 c, according to anembodiment of the present invention. Alternatively, the flow chart ofFIG. 6 may be viewed as depicting steps of an example of a methodimplemented in the optical disc drive 100 (FIG. 1) to calibrate thepower of the laser 140 (FIG. 1) for use in writing a label to the labelsurface of the optical disc 136 (FIG. 1).

The laser power calibration system 159 c employs a “walk-up” approach todetect the ankle 186 (FIG. 3) of the reflectivity curve depicted in FIG.3. Beginning with box 303, the laser power setting is set at an initialpredefined value that causes the laser 140 to deliver a quantum ofradiant energy to segments to be marked on the optical disc 136resulting in a reflectivity on the reflectivity curve that is located tothe left of the knee 183. Such a value may be, for example, the lowestpossible laser power setting such as the reflectivity read setting.Thereafter, in box 306 a first calibration pattern of marked segments173 (FIG. 2) is written to the respective track 169 (FIG. 2) of theoptical disc 136. Alternatively, the calibration pattern 166 (FIG. 2)may be written to multiple tracks such as is the case, for example, whenthe calibration pattern 166 is written over the segments of an image tobe written to the label surface of the optical disc 136 as describedabove.

Thereafter, in box 309, the reflectivity of the marked segments 173 ofthe calibration pattern 166 are measured and stored in the memory 116(FIG. 1). Also, these measurements may be adjusted for noise bysubtracting reflectivity measurements of unmarked segments for a givenoptical disc 136 as was described with reference to box 206 (FIG. 4)above. In this respect, measurements of the reflectivity of unmarkedsegments may be taken from the optical disc 136 in a manner as discussedin box 201 (FIG. 4) above. In box 313, the average reflectivity of themarked segments 173 stored in the memory 116 is calculated. Thus, eachof the marked segments 173 is marked with the laser 140 set at a singlelaser power setting, thereby applying the same quantum of radiant energyto each of the marked segments 173. The average reflectivity calculatedin box 313 is for each of the marked segments 173 that were created withthe same quantum of radiant energy. In box 316, the laser powercalibration system 159 c implements a rewrite of the calibration pattern166 over the previously marked segments 173. This is done after asuitable period of time has elapsed for cooling of the marked segmentsfrom the writing of the calibration pattern 166 in box 306 to preventablation.

In box 319, once again the reflectivity of the marked segments 173 ismeasured and stored in the memory 116. Also, in box 323 the averagereflectivity of the marked segments 173 is calculated and stored in thememory 116. Next, in box 326, a reflectivity differential is calculatedbetween the previous and the current average reflectivities calculatedin boxes 313 and 326. Thereafter, in box 329, it is determined whetherthe knee 183 has already been detected. If not, then the laser powercalibration system 159 c proceeds to box 333. Otherwise, the laser powercalibration system 159 c progresses to box 336.

In box 333, the laser power calibration system 159 c determines whetherthe difference calculated in box 326 is greater than a predefinedthreshold. In this respect, once the reflectivity differentialincreases, then it may be assumed that the knee 183 has been detectedsince the reflectivity remains rather flat to the left of the knee 183.The predefined threshold may be, for example, a predefined percentageincrease over the lowest previous measurement of the reflectivity usedto calculate the reflectivity differential in box 326. The predefinedpercentage or other threshold value may be stored in memory, etc.Assuming that the knee 183 has been detected in box 333, then the laserpower calibration system 159 c proceeds to box 339. Otherwise, the laserpower calibration system 159 c reverts back to box 316.

Assuming that the laser power calibration system 159 c has detected theknee 183 in box 333, then in box 339 the laser power setting associatedwith the knee 183 is stored for future use. Thereafter, the laser powercalibration system 159 c proceeds to box 336. In box 336, the laserpower calibration system 159 c detects whether the ankle 186 has beenlocated. Once the knee 183 has been detected in box 333, the ankle 186may be detected by determining whether the current reflectivitydifferential is less than a predefined threshold. In this respect, giventhat the reflectivity decreases with increasing laser power setting inthe region of reliable reflectivity 189 (FIG. 3) as described above,then with each increasing write operation over the marked segments usingthe same laser setting, when in the region of reliable reflectivity 189,the reflectivity should decrease in a generally linear fashion.

Thus as the ultimate quantum of radiant energy from multiple writes isapplied to the marked segments 173, with each write operation performed,the reflectivity should be reduced while the laser power settings resultin reflectivities within the reliable region of reflectivity 189. Whenthe reflectivity is no longer reduced from one measurement to the nextfor consecutive reflectivities, then it may be assumed that the laserpower setting is at or to the right of the ankle 186, thereby accountingfor the lack of reduction in the reflectivity. Thus, a predefineddifference threshold is stored in the memory 116 that equals a minimumchange in the reflectivity expected between two consecutive laser powersettings in the region of reliable reflectivity 189. When thereflectivity difference between previous and current averagereflectivities obtained in either block 313 or 326 is less than thepredefined threshold difference, it is assumed that the quantum ofradiant energy applied to the marked segments 173 corresponds with alaser power setting that places the reflectivity beyond the ankle 186.

Thus, in box 336, if the reflectivity differential is less than thepredefined threshold difference such that the ankle 186 is detected,then the laser power calibration system 159 c proceeds to box 343 inwhich the laser power setting is set at the optimal laser settingrelative to the laser power settings determined at the knee 183 and theankle 186 as was described with reference to box 233 (FIG. 4) above.Thereafter, the laser power calibration system 159 c ends and the laserpower setting is employed to write the ultimate label to the labelsurface of the optical disc 136.

However, if the ankle 186 is not detected in box 336, then the laserpower calibration system 159 c reverts to box 316 to rewrite anadditional calibration pattern 166 over the marked segments.

With these concepts in mind, reference is made to FIG. 7 that depicts agraph of darkness of marked segments 173 as a function of the laserpower setting. The graph includes an initial darkness curve C₁ thatshows darkness as a function of the laser power setting when the opticaldisc drive 100 is first manufactured. In particular, a test may beperformed to obtain the initial darkness curve C₁ in which a pattern iswritten, for example, to a track 169 of a test optical disc 136 thatincludes a repeated array of segments showing a range darkness writtento the disc using laser power settings ranging from the minimum possibleto the maximum possible. Alternatively, the track 169 may be written toseveral optical discs 136 to obtain data from multiple optical discs136. Once the pattern is written, the darkness of the segments may bemeasured using a photo spectrometer. Thereafter, the initial darknesscurve C₁ may be generated. Thereafter, an initial laser power setting P₁is selected for operation of the optical disc drive 100 in writinglabels to the label surfaces of optical discs 136 based upon a desireddarkness.

Over time, however, the darkness curve will shift to the right as thelaser power is absorbed, for example, by dust collecting on a lensassociated with the laser 140 and due to other factors discussed above.Consequently, over time the quantum of radiant energy delivered to agiven segment by the laser 140 at the initial laser power setting P₁will diminish over time. In this respect, the initial darkness curve C₁may “shift” to the right on the graph shown in FIG. 7 as shown by thedarkness curve C₂. Note that it may be the case that the shape of thedarkness curve C₂ may differ from the shape of the curve C₁, where thecurves C₁ and C₂ are provide merely purposes of illustration.

With this in mind, reference is made to FIG. 8 that shows a flow chartthat provides one example of the operation of the laser powercalibration system 159, denoted herein as laser power calibration system159 d, according to an embodiment of the present invention.Alternatively, the flow chart of FIG. 8 may be viewed as depicting stepsof an example of a method implemented in the optical disc drive 100(FIG. 1) to calibrate the power of the laser 140 (FIG. 1) for use inwriting a label to the label surface of the optical disc 136 (FIG. 1).As will be described, the laser power calibration system 159 ddetermines a laser power setting that results in a predefined darknesson the label surface of the optical disc 136.

Beginning with box 353, the laser power calibration system 159 dimplements the measurement of an approximate maximum reflectivity orminimum darkness of the optical disc 136. This measurement is done withthe laser power set at the “reflectivity read” setting as describedabove. The measurement of the maximum reflectivity of the optical disc136 may be performed by moving the optical pickup unit 123 (FIG. 1) suchthat the laser 140 is directed to a nearly 100% reflective surface ofthe optical disc 136 such as an internal ring on the optical disc 136 ascan be appreciated by those in ordinary skill in the art. Once theapproximation of the maximum reflectivity is measured, it is then storedin the memory 116 (FIG. 1) for future use.

Thereafter, in box 356, a measurement of an approximate minimumreflectivity detectable by the sensor 141 (FIG. 1) is taken at thereflectivity read laser power setting that is either focused at aposition of known maximum darkness on the optical disc 136, or thelenses associated with the laser 140 are defocused such that little orno laser light is reflected back to the sensor 141. The minimumreflectivity is then stored in the memory 116. Thus, a range ofreflectivity of the optical disc 136 is established from the minimum andmaximum reflectivities determined in boxes 353 and 356 above.

Next, in box 359 the laser power calibration system 159 d implements thewriting of a calibration pattern 166 of marked segments to the opticaldisc 136. As discussed above, the calibration pattern 166 may be writtento a predefined track 169 or may be written over segments thatcorrespond to those that are part of the image to be written to thelabel surface of the optical disc 136 itself. The calibration pattern166 may comprise, for example, the array of marked segments that arecreated with different quanta of radiant energy from the laser 140 thatis set at correspondingly different laser power settings. Such an arraywould be repeated around the circumference of the track 169 or withinsegments that coincide with the pixels of the image to be written to thelabel surface.

Then, in box 363, the reflectivity of each of the marked segments ismeasured and stored in the memory 116 in an association with thecorresponding laser power settings that were employed to write suchmarked segments as a part of the calibration pattern 166 in box 359above. Thereafter, in box 366, an average reflectivity is calculated foreach laser power setting employed to generate the marked segments basedupon the reflectivity measurements of each of the marked segments 173(FIG. 2). In this respect, the average reflectivity calculated for eachlaser power setting falls within the range of reflectivity establishedin boxes 353 and 356 above. The average reflectivities determinedprovide the basis for a curve that depicts the average reflectivity as afunction of laser power setting similar to the curve of FIG. 3, with theexception that the average reflectivity is shown rather than thereflectivity.

Thereafter in box 369 the laser power setting at the knee 183 (FIG. 3),denoted as P_(Knee), is determined by analyzing the averagereflectivities to locate the laser power setting at which the bend ofthe knee 183 occurs. Then, in box 373, a slope M₁ of the averagereflectivity/power curve is determined to the right of the knee 183 byanalyzing the average reflectivities along the slope of the averagereflectivity/power curve. In this respect, the slope M₁ is determined ata location on the curve where the average reflectivity decreases withincreasing laser power. In one embodiment, the slope M₁ is determinedbetween the knee 183 and the ankle 186 (FIG. 3). Once the laser powersetting P_(Knee) and the slope M₁ are known, then the desired or targetlaser power setting that results in a target or predefined desireddarkness, denoted target darkness D_(Tar), is determined.

In this respect, the target darkness D_(Tar) is determined empiricallyby marking segments on optical discs 136 and measuring the darkness ofthese segments using a photo spectrometer in a laboratory environment,etc. For greater accuracy, multiple measurements of the darkness atvarious laser power settings may be averaged as can be appreciated. Inthe same manner, a darkness may be determined empirically at the knee183, denoted herein as darkness D_(Knee). Also, in addition to measuringthe darkness of the marked segments, empirical measurements of thereflectivity may also be obtained in a laboratory environment. Thus,from a number of marked segments, a curve may be generated representingthe darkness as a function of laser power. Also, a curve representingthe reflectivity as a function of laser power may be generated. The datafrom these curves may be combined to create a curve that depicts thereflectivity as a function of darkness or vice versa. From this combinedcurve, an approximation of a slope M₂ may be obtained of thereflectivity vs. darkness curve. This slope may comprise, for example,the reflectivity as a function of darkness obtained at locations betweenthe knee 183 and the ankle 186.

Thereafter, the target or desired power at which the laser power settingis to be set for general operation may be calculated as follows:

Target Power=M ₁ M ₂(D _(Tar) −D _(Knee))+P _(Knee).

In this respect, given that the slope M₁ is expressed in terms ofPower/Reflectivity and the slope M₂ is expressed in terms ofReflectivity/Darkness, then their product is Power/Darkness. This valuemultiplied by the value calculated from (D_(Tar)−D_(Knee)) results inlaser power.

Thus, in box 376, the target power at which the laser power setting isto be set in order to write a label to the label surface of the opticaldisc 136 is calculated as set forth above. Thereafter, in box 379, thelaser power setting of the laser 140 is set relative to the target powerto write the label to the label surface of the optical disc 136. In thisrespect, the laser power setting may be set at or near the target power,or at some predefined interval relative to the target power. Thereafter,the laser power calibration system 159 d ends as shown.

With reference to FIG. 9, shown is a graph that depicts a reflectivityof segments 173 as a function of the voltage detected at the sensor 141(FIG. 1). Generally the voltage generated by the sensor 141 isproportional to the reflectivity of a given segment 173. This is due tothe fact that the voltage is generally proportional to reflected laserlight 143 that falls onto the sensor 141. The reflected laser light 143,in turn, is proportional to the reflectivity at a given segment 173 onthe optical disc 136. The maximum reflectivity R_(Max) is thatreflectivity detected from a location or segment of maximum reflectionon the optical disc 136. This point may be found, for example, on ahighly reflective inner ring of the optical disc 136 as can beappreciated.

The minimum reflectivity R_(Min) is a minimum reflection that may beobtained from an optical disc 136. This point may be found, for example,by defocusing the laser 140 such that no reflected laser light 143 fallsonto the sensor 141. Alternatively, the laser 140 may be pointed to alocation or segment of maximum darkness on the optical disk 136 toobtain a reading of the minimum reflectivity R_(Min). Note that theminimum reflection is greater than a zero reflection due to the factthat the sensor may detect some reflected light and due to processvariation in the manufacture of the sensors 141 themselves. Between themaximum and minimum reflectivities R_(Max) and R_(Min) is a predefinedrange of reflectivity 390 relative to the optical disc 136 in theoptical disc drive 100. Within the predefined range of reflectivity 390is an operating range R_(Op). The operating range R_(Op) is the range ofreflectivity that is expected when a segment of a desired darkness iswritten to the optical disc 136. Thus, in one embodiment, thecalibration of the laser power involves setting the laser power toensure that the resulting reflectivity of marked segments 173 (FIG. 2)fall within the operating range R_(Op).

Referring next to FIG. 10, shown is a flow chart that provides oneexample of the operation of the laser power calibration system 159,denoted herein as laser power calibration system 159 e, according to anembodiment of the present invention. Alternatively, the flow chart ofFIG. 10 may be viewed as depicting steps of an example of a methodimplemented in the optical disc drive 100 (FIG. 1) to calibrate thepower of the laser 140 (FIG. 1) for use in writing a label to the labelsurface of the optical disc 136 (FIG. 1). The flow chart of FIG. 10involves the calibration of the laser power as falling within theoperating range R_(Op) of the predefined range of reflectivity 390.

In boxes 403 and 406, the maximum reflectivity and minimum reflectivityare both obtained in a manner similar to that discussed with referenceto boxes 353 and 356 of FIG. 8. Thereafter, in box 409, the laser powersetting is set at an initial power setting at which it is believed theresulting reflectivity will fall within the operating range R_(Op). Thissetting may be, for example, a setting that is predefined in the memory116 based upon measurements at the time of manufacture of the opticaldisc drive 100. Alternatively, the laser power setting may be set at thepower setting at which a previous label was written to a prior opticaldisc 136.

Next, in box 413, a calibration pattern 116 that comprises a stitchpattern is written to at least a portion of a given track 169. Thestitch pattern includes a number of pairs of marked and unmarkedsegments. The respective unmarked and marked segments in a given pairmay be adjacent to each other or they may be separated by a number ofsegments. In one embodiment, the unmarked and marked segments withineach pair are adjacent to each other so that they are formed within thesame region of the label surface of the optical disc 136 such that thereis little variation in the nature of the chemical coating between thetwo segments 173, given that there may be process variation in thethickness and chemical makeup of the coating itself between differentregions of the disc.

Alternatively, where the marked and unmarked segments within a givenpair are not adjacent to each other, then they may be located within thesame general region of an optical disc 136 so as to ensure that anyvariation in the coating on the label surface is minimal with respect toboth the marked and unmarked segments within a given pair of segments.

Thereafter, in box 416, the reflectivities of all unmarked and markedsegments associated with the given pairs in the stitch pattern writtento the disc as the calibration pattern in box 413 are measured andstored in the memory 116. Thereafter, in box 419, the laser calibrationsystem 159 e calculates an averaged unmarked reflectivity and an averagemarked reflectivity from all of the unmarked and marked segments of therespective pairs of the stitch pattern. In this respect, the averageunmarked reflectivity and the average marked reflectivity providesreflectivity measurements that are taken from multiple positions on theoptical disc 136 that should negate any process variation in nature ofthe coating applied to the label surface. Alternatively, select markedand unmarked reflectivities measured in box 416 may be employed ratherthan performing averaging as described in box 419. However, suchnon-averaged values may be susceptible to variation due to processvariation in the manufacture of the label surface. In such a case, box419 may be omitted.

Then, in box 423, an average reflectivity difference is calculatedbetween the average unmarked reflectivity and the average markedreflectivity. This may be done, for example, by subtracting the averagemarked reflectivity from the average unmarked reflectivity.Alternatively, the reflectivity difference may be calculated fromnon-averaged reflectivities obtained in box 416 as described above,where the reflectivity difference is not an average reflectivitydifference. Thus, one embodiment, the average reflectivity differencemay not actually be an averaged difference. Next, in box 426, apercentage of the predefined range of reflectivity represented by theaverage reflectivity difference is determined. In this respect, thepercentage of the reflectivity difference of the total predefined rangeof reflectivity 390 from the maximum reflectivity R_(Max) to the minimumreflectivity R_(Min) as described above with reference to FIG. 9. To doso, the minimum reflectivity R_(Min) is subtracted from the averagereflectivity difference. The remainder of the average reflectivitydifference is divided by the magnitude of the predefined range ofreflectivity 390 from the maximum reflectivity R_(Max) to the minimumreflectivity R_(Min).

Thereafter, in box 429, the laser power calibration system 159 edetermines whether the percent reflectivity calculated in box 426 is toolow such that it falls below the operating range R_(Op). If such is thecase then the laser calibration system 159 e progresses to box 433.Otherwise, the laser power calibration system 159 e proceeds to box 436.

In box 436, the laser power calibration system 159 e determines whetherthe percent reflectivity is too high such that it falls above theoperating range R_(Op). If such is the case, then the laser powercalibration system 159 e proceeds to box 439. Otherwise, the laser powercalibration system 159 e proceeds to box 443.

Assuming that the laser power calibration system 159 e has progressed tobox 433, then the laser power setting is increased by a predefinedincrement. Such an increment may comprise, for example, 10% of the totalpossible adjustment of the laser power setting or other appropriatedesign specific increment. In any event, the increment applied should besmall enough such that the resulting reflectivity range associated withthe increment itself is less than the operating range R_(Op).

Alternatively, assuming that the laser power calibration system 159 ehas proceeded to box 439, then the laser power setting of the laser 140is decreased by a predefined increment. Regardless of whether the laserpower setting is increased or decreased by the predefined increment asset forth in box 433 or 439, the laser power calibration system 159 ethen reverts back to box 413 to write an additional stitch pattern onthe optical disc 136. In this respect, the laser power calibrationsystem 159 e repeatedly adjusts the laser power setting and rewritesstitch patterns on the optical disc 136 until the reflectivitydifference between the marked and unmarked segments of the respectivestitch patterns results in a percent reflectivity change that fallswithin the operating range R_(Op) as described above.

In some embodiments, the same track 169 on an optical disc 136 mayaccommodate multiple stitch patterns, given that the laser powercalibration system 159 e may write multiple stitch patterns to theoptical disc 136 as described above. In this respect, the stitchpatterns may be interleaved with respect to each other. Also, the sameunmarked segments may be employed for multiple different stitchpatterns. Specifically, the marked segment of each pair that includes anunmarked segment common to multiple stitch patterns is writtenrelatively close to the unmarked segment so as to ensure as littleprocess variation in the coating on the label surface as is possiblebetween the marked and unmarked segment of a respective pair. In thisrespect, a single track 169 may accommodate the writing of manydifferent stitch patterns in the attempt to calibrate the power of thelaser 140. As a result, the use of multiple tracks 169 for purposes ofwriting the calibration patterns may be avoided, thereby eliminating anypotential negative effect on the appearance of the label to be printedto the optical disc 136. In an additional alternative, the stitchpatterns may be written to segments that coincide with the pixels thatcomprise part of the label to be written to the label surface of theoptical disc 136.

Assuming that the laser power calibration system 159 e has proceeded tobox 443, then the new power setting is stored for operation of the laser140 in writing the label to the label surface of the optical disc 136.In this respect, the laser power setting is the last laser power settingemployed to write a stitch pattern to the optical disc 136 as describedabove. Thereafter, the laser power calibration system 159 e ends asshown.

Referring next to FIG. 11, shown is a flow chart that provides oneexample of the operation of the laser power calibration system 159,denoted herein as laser power calibration system 159 f, according to anembodiment of the present invention. Alternatively, the flow chart ofFIG. 11 may be viewed as depicting steps of an example of a methodimplemented in the optical disc drive 100 (FIG. 1) to calibrate thepower of the laser 140 (FIG. 1) for use in writing a label to the labelsurface of the optical disc 136 (FIG. 1).

Beginning with box 453, the laser power calibration system 159 fpositions the laser 140 over a calibration segment on the optical disc136, where the segment may be, for example, a single pixel. In thisregard, the laser 140 is held stationary relative to the optical disc136 over the calibration segment. Next, in box 454, a measurement of thenoise associated with the measuring of the reflectivity is obtained.This is done by taking a measurement of the reflectivity with the laser140 (FIG. 1) turned off. In this respect, the signal from the sensor 141(FIG. 1) is generated by noise from either a reflectivity of the opticaldisc 136 and due to electrical noise associated with the operation ofthe sensor 141 and other electrical components. Thereafter, in box 456,the laser power calibration system 159 f starts a timer. In thisrespect, the timer may be a software component stored within the memory116 (FIG. 1) as a portion of the laser power calibration system 159 f.Alternatively, a hardware timer may be employed.

Next, in box 459, a laser 140 is activated at the current power setting.This may be, for example, the power setting employed to write a previouslabel to the label surface of a prior optical disc 136. Alternatively,some other laser power setting may be employed. Concurrent with theactivation of the laser 140, the laser power calibration system 159 fmeasures a reflectivity of the calibration segment. In this respect, themeasuring of the reflectivity of the calibration segment is implementedconcurrent with the application of the laser beam generated by the laser140 to the calibration segment. When the laser 140 is initiallyactivated, a highest reading of the reflectivity is obtained and stored.From this reading, the noise measured in box 454 is subtracted from thishighest reading. Next, in box 463, the laser power calibration systemdetermines whether the reflectivity of the calibration segment hasfallen below a predefined reflectivity threshold stored in the memory116.

This predefined reflectivity threshold may be, for example, a predefinedpercentage, for example, 10% of a reflectivity range extending from thenoise measured in box 454 on the low side to the highest reflectivityobtained when the laser 140 was initially turned on in box 459.Alternatively, the predefined reflectivity threshold may be, forexample, an approximation of the lowest possible reflectivity within therange of reliable reflectivity 189 (FIG. 3) or other value stored in thememory 116 of the optical disc drive 100. However, such a value issubject to inaccuracy due to the change in noise and degradation in thepower of the laser 140 over time. In any event, once the reflectivityfalls below the predefined reflectivity threshold in box 463, then inbox 466 the laser power calibration system 159 f stops the timer thatwas started in box 456 above. In this respect, the laser powercalibration system 159 f tracks a time for the reflectivity of thecalibration segment to drop below the predefined reflectivity thresholdof box 463 during the application of the laser beam to the calibrationsegment.

Next, in box 469, the laser power calibration system 159 f determineswhether the total time it took for the reflectivity to drop below thepredefined reflectivity threshold is less than a lower limit of anoperating range of time that is stored in the memory 116. In thisrespect, the operating range of time provides a window of time withinwhich the reflectivity should drop below the reflectivity threshold inbox 463. The operating range of time may be determined byexperimentation. If the time it takes for the reflectivity to drop belowthe reflectivity threshold is less than the lower limit of the operatingrange of time, then the laser power setting should be decreased so thatit takes a greater amount of time for the reflectivity of the textsegment to drop below the reflectivity threshold in box 463.

On the other hand, if the time of operation is greater than an upperlimit of the operating range of time, then the laser power should beincreased so as to ensure that the reflectivity drops below thereflectivity threshold in box 463 within the operating range of time.Thus, in box 469, it is determined whether the time it took for thereflectivity to drop below the reflectivity threshold in box 463 isgreater than the operating range of time. If such is the case then thelaser power calibration system 159 f proceeds to box 473. Otherwise, thelaser power calibration system 159 f proceeds to box 476.

Assuming that the laser power calibration system 159 f has proceeded tobox 476, then it is determined whether the time it took for thereflectivity to drop below the reflectivity threshold in box 463 is lessthan the operating range of time. If such is the case then the laserpower calibration system 159 f proceeds to box 479. Otherwise the laserpower calibration system 159 f proceeds to box 483.

Assuming that the laser power calibration system 159 f has proceeded toeither box 473 or box 479, then the time it took for the reflectivity todrop below the reflectivity threshold in box 453 is either less than orgreater than the operating range of time. Thus, in box 473, the laserpower is increased by a predefined increment. Conversely, in box 479 thelaser power setting of the laser 140 is decreased by a predefinedincrement. In this respect, the increment by which the laser powersetting is increased or decreased is design specific. For example, anincrease or decrease of 10% of the total range of laser power settingsmay be applied. From either box 473 or box 479, the laser powercalibration system 159 f proceeds to box 486 in which the laser 140 ispositioned over a subsequent calibration segment on the optical disc136.

Thereafter, the laser power calibration system 159 f moves to box 489 inwhich the timer is reset for operation. Next, the laser powercalibration system 159 f reverts back to box 454 in which thecalibration cycle is performed a subsequent time in order to determinewhether the alteration of the laser power in either box 473 or 479causes the ultimate time it takes for the reflectivity to drop below thethreshold in box 463 to fall within the operating range of time asdescribed.

Assuming that the laser power calibration system 159 f has proceeded tobox 483, then the time it took for the reflectivity to drop below thereflectivity threshold in box 463 fell within the operating range oftime. As such, the new power setting obtained is stored in the memory116 and applied to the laser 140 for normal operation in writing labelsto the label surface of the optical disc. Thereafter, the laser powercalibration system 159 f ends as shown.

Although the various embodiments of the laser power calibration system159 are depicted as being embodied in software or code executed bygeneral purpose hardware as discussed above, as an alternative each ofthe various embodiments of the laser power calibration system 159 mayalso be embodied in dedicated hardware or a combination ofsoftware/general purpose hardware and dedicated hardware. If embodied indedicated hardware, each one of the various embodiments of the laserpower calibration system 159 can be implemented as a circuit or statemachine that employs any one of or a combination of a number oftechnologies. These technologies may include, but are not limited to,discrete logic circuits having logic gates for implementing variouslogic functions upon an application of one or more data signals,application specific integrated circuits having appropriate logic gates,programmable gate arrays (PGA), field programmable gate arrays (FPGA),or other components, etc. Such technologies are generally well known bythose skilled in the art and, consequently, are not described in detailherein.

The flow charts of FIGS. 4-6, 8, 10, and 11 show the architecture,functionality, and operation of an implementation of the variousembodiments of the laser power calibration system 159. If embodied insoftware, each block may represent a module, segment, or portion of codethat comprises program instructions to implement the specified logicalfunction(s). The program instructions may be embodied in the form ofsource code that comprises human-readable statements written in aprogramming language or machine code that comprises numericalinstructions recognizable by a suitable execution system such as aprocessor in a computer system or other system. The machine code may beconverted from the source code, etc. If embodied in hardware, each blockmay represent a circuit or a number of interconnected circuits toimplement the specified logical function(s).

Although flow charts of FIGS. 4-6, 8, 10, and 11 show a specific orderof execution, it is understood that the order of execution may differfrom that which is depicted. For example, the order of execution of twoor more blocks may be scrambled relative to the order shown. Also, twoor more blocks shown in succession in FIGS. 4-6, 8, 10, and 11 may beexecuted concurrently or with partial concurrence. In addition, anynumber of counters, state variables, warning semaphores, or messagesmight be added to the logical flow described herein, for purposes ofenhanced utility, accounting, performance measurement, or providingtroubleshooting aids, etc. It is understood that all such variations arewithin the scope of the present invention.

Also, where the various embodiments of the laser power calibrationsystem 159 comprise software or code, each can be embodied in anycomputer-readable medium for use by or in connection with an instructionexecution system such as, for example, a processor in a computer systemor other system. In this sense, the logic may comprise, for example,statements including instructions and declarations that can be fetchedfrom the computer-readable medium and executed by the instructionexecution system. In the context of the present invention, a“computer-readable medium” can be any medium that can contain, store, ormaintain the various embodiments of the laser power calibration system159 for use by or in connection with the instruction execution system.The computer readable medium can comprise any one of many physical mediasuch as, for example, electronic, magnetic, optical, electromagnetic,infrared, or semiconductor media. More specific examples of a suitablecomputer-readable medium would include, but are not limited to, magnetictapes, magnetic floppy diskettes, magnetic hard drives, or compactdiscs. Also, the computer-readable medium may be a random access memory(RAM) including, for example, static random access memory (SRAM) anddynamic random access memory (DRAM), or magnetic random access memory(MRAM). In addition, the computer-readable medium may be a read-onlymemory (ROM), a programmable read-only memory (PROM), an erasableprogrammable read-only memory (EPROM), an electrically erasableprogrammable read-only memory (EEPROM), or other type of memory device.

Although the invention is shown and described with respect to certainembodiments, it is obvious that equivalents and modifications will occurto others skilled in the art upon the reading and understanding of thespecification. The present invention includes all such equivalents andmodifications, and is limited only by the scope of the claims.

1-49. (canceled)
 50. A method for calibrating an optical disc drive,comprising the steps of: writing a calibration pattern of markedsegments to an optical disc; measuring at least one reflectivity of themarked segments for each one of a plurality of laser power settings,thereby obtaining a curve that depicts the reflectivity with respect tothe laser power settings using the at least one reflectivity for eachone of the laser power settings; identifying the laser power setting ata knee of the curve; and calibrating the optical disc drive based atleast in part upon the laser power setting at the knee.
 51. The methodof claim 50, wherein the step of identifying the laser power setting atthe knee of the curve further comprises the steps of: detecting at leastone of the reflectivities that falls to the right of the knee of thecurve; and detecting at least one of the reflectivities that falls tothe left of the knee of the curve.
 52. The method of claim 50, furthercomprising the steps of setting the laser power setting at a valuerelative to the location of the knee of the curve to write a label on anoptical disc.
 53. The method of claim 50, further comprising the stepsof: determining a slope of the curve at a position on the curve wherethe reflectivity decreases as the laser power settings increase; andidentifying the laser power setting at an ankle of the curve; andwherein the step of determining the slope of the curve further comprisesdetermining the slope of the curve between the knee and the ankle. 54.The method of claim 50, wherein the step of writing the calibrationpattern of marked segments to the optical disc further comprises writingan array of marked segments to the optical disc, wherein the array ofmarked segments includes marked segments written by the laser atmultiple laser power settings.
 55. The method of claim 54, wherein thearray of marked segments is written in a stair step configuration. 56.The method of claim 50, further comprising the step of adjusting the atleast one reflectivity of the marked segments to account for noise dueto process variation in a coating on a label surface of an optical disc.57. A laser power calibration system for calibrating an optical discdrive, comprising: a processor circuit having a processor and a memory;a laser operatively coupled to the processor circuit, the laser beingadapted to write a label to a label surface of an optical disc placed inthe optical disc drive; a sensor operatively coupled to the processorcircuit, the sensor being adapted to measure a reflectivity atdesignated segments on the optical disc; a laser power calibrationsystem stored in the memory and executable by the processor, the laserpower calibration system comprising: logic that writes a calibrationpattern of marked segments to the label surface of the optical disc;logic that measures at least one reflectivity of the marked segments foreach one of a plurality of laser power settings, thereby obtaining acurve that depicts the reflectivity with respect to the laser powersettings using the at least one reflectivity for each one of the laserpower settings; logic that identifies the laser power setting at a kneeof the curve; and logic that calibrates the optical disc drive based atleast in part upon the laser power setting at the knee.
 58. The laserpower calibration system of claim 57, wherein the laser powercalibration system further comprises logic that sets the laser powersetting at a value relative to the location of the knee of the curve towrite the label to the label surface of the optical disc.
 59. A methodfor calibrating an optical disc drive, comprising the steps of: writinga calibration pattern of marked segments to an optical disc; measuring areflectivity of each of the marked segments; generating an averagereflectivity for each one of a plurality of laser power settings,thereby obtaining a curve that depicts the average reflectivity withrespect to the laser power settings; identifying the laser power settingat a knee of the curve; and calibrating the optical disc drive based atleast in part upon the laser power setting at the knee.
 60. The methodof claim 59, wherein the step of identifying the laser power setting atthe knee of the curve further comprises the steps of: detecting at leastone of the average reflectivities that falls to the right of the knee ofthe curve; and detecting at least one of the average reflectivities thatfalls to the left of the knee of the curve.
 61. The method of claim 59,further comprising the steps of setting the laser power setting at avalue relative to the location of the knee of the curve to write a labelon an optical disc.
 62. The method of claim 59, further comprising thesteps of: determining a slope of the curve at a position on the curvewhere the average reflectivity decreases as the laser power settingsincrease; and identifying the laser power setting at an ankle of thecurve; and wherein the step of determining the slope of the curvefurther comprises determining the slope of the curve between the kneeand the ankle.
 63. The method of claim 59, wherein the step of writingthe calibration pattern of marked segments to the optical disc furthercomprises writing an array of marked segments to the optical disc,wherein the array of marked segments includes marked segments written bythe laser at multiple laser power settings.
 64. The method of claim 63,wherein the array of marked segments is written in a stair stepconfiguration.
 65. The method of claim 59, further comprising the stepof adjusting the reflectivity of each of the marked segments to accountfor noise due to process variation in a coating on a label surface of anoptical disc.
 66. A laser power calibration system for calibrating anoptical disc drive, comprising: a processor circuit having a processorand a memory; a laser operatively coupled to the processor circuit, thelaser being adapted to write a label to a label surface of an opticaldisc placed in the optical disc drive; a sensor operatively coupled tothe processor circuit, the sensor being adapted to measure areflectivity at designated segments on the optical disc; a laser powercalibration system stored in the memory and executable by the processor,the laser power calibration system comprising: logic that writes acalibration pattern of marked segments to the label surface of theoptical disc; logic that measures the reflectivity of each of the markedsegments; logic that generates an average reflectivity for each one of aplurality of laser power settings, thereby obtaining a curve thatdepicts the average reflectivity with respect to the laser powersettings; logic that identifies the laser power setting at a knee of thecurve; and logic that calibrates the optical disc drive based at leastin part upon the laser power setting at the knee.
 67. The laser powercalibration system of claim 66, wherein the logic that identifies thelaser power setting at the knee of the curve further comprises: logicthat detects at least one of the average reflectivities that falls tothe right of the knee of the curve; and logic that detects at least oneof the average reflectivities that falls to the left of the knee of thecurve.
 68. The laser power calibration system of claim 66, wherein thelaser power calibration system comprising further comprises logic thatsets the laser power setting at a value relative to the location of theknee of the curve to write a label on an optical disc.
 69. The laserpower calibration system of claim 66, wherein the laser powercalibration system comprising further comprises: logic that determines aslope of the curve at a position on the curve where the averagereflectivity decreases as the laser power settings increase; and logicthat identifies the laser power setting at an ankle of the curve; andwherein the logic that determines the slope of the curve furthercomprises determines the slope of the curve between the knee and theankle.
 70. The laser power calibration system of claim 66, wherein thelaser power calibration system comprising further comprises logic thatadjusts the reflectivity of each of the marked segments to account fornoise due to process variation in a coating on the label surface of theoptical disc.